Data illustrating a stimulatory role for dopamine and an inhibitory role for opioids in sexually-motivated song. Mean measures of song produced by male starlings after peripherally administered vehicle treatment (open bars) and drug treatment (dark bars) with A) the D1 dopamine receptor antagonist SCH 23390, B) the dopamine reuptake inhibitor GBR-12909, C) the opioid receptor antagonist naloxone, and D) the mu opioid receptor agonist fentanyl. *Indicates p < 0.05. See text for additional detail. Figures redrawn from Riters et al., 2005 and Schroeder and Riters, 2006.